Field of the Invention
This invention relates to magnetostatic wave devices and more particularly to a magnetostatic wave delay line having a predetermined linear or quadratic phase variation over a predetermined frequency range.
Description of the Prior Art
In U.S. Pat. No. 4,314,214, which issued on Feb. 2, 1982 to J. P. Castera, P. Hartemann, and J. M. DuPont, a magnetostatic-wave device is described comprising a ferromagnetic layer for propagating magnetostatic waves along a path and an array of conductive strips positioned on the ferromagnetic layer such as shown in FIG. 1. Current is induced into the conducting strips by magnetostatic waves passing underneath these strips.
In U.S. Pat. No. 3,935,550, which issued on Jan. 27, 1976 to J. D. Adam, the inventor herein, and J. H. Collins, a group delay equalizer was described incorporating a magnetostatic delay line such as shown in FIGS. 3A through 3C. In FIG. 7, a delay line is shown comprising YIG film 23 separated from a brass ground plane 22 by a dielectric layer 21. The dielectric layer 21 is formed from Gadolinium Gallium Garnet (GGG) on which the YIG film 23 was grown. FIG. 8 shows three curves 38 through 40 of delay per centimeter versus frequency over the frequency range 1 to 1.5 gigahertz calculated from equation (2) for a device having the dimensions D of 50 microns for dielectric spacing and T of 7 micrometers for YIG film thickness. At bias fields of 0, 20 and 40 Oersted respectively.
In U.S. Pat. No. 3,864,647, which issued on Feb. 4, 1975 to W. L. Bongianni, non-dispersive and linearly dispersive magnetic delay lines are described. FIG. 3 shows a delay line with magnetic wave active material 24 and 28 on either side of magnetic wave inactive material 22. FIG. 6 shows a delay line with a ground plane 48 covered by a layer of magnetic wave inactive material 46 covered by a layer of magnetic wave active material 44 covered with a layer of magnetic wave inactive material 42 covered with a layer of magnetic wave active material 41. FIG. 6 shows a linearly dispersive magnetic delay line.
It is therefore desirable to provide a magnetostatic wave device having a delay which varies linearly with frequency or is constant with frequency.
It is further desirable to provide a magnetostatic wave device having a medium suitable for propagating magnetostatic waves and a first and second ground plane, side by side, each having a predetermined spacing from the medium and each having a predetermined length along the propagation path.
It is further desirable to provide a magnetostatic wave device having a medium suitable for propagating magnetostatic waves and a ground plane having a continuous variation in spacing other than a linear variation in spacing to get a minimum phase error with respect to a quadratic phase variation with frequency.
It is further desirable to provide a magnetostatic wave device comprising a plurality of sections wherein each section has a medium suitable for propagating magnetostatic waves and a ground plane spaced by a predetermined distance from its respective medium and having a predetermined length along the propagation path.
It is further desirable to provide a dispersive delay line utilizing a yttrium iron garnet (YIG) film and a ground plane having a plurality of spacings from the YIG film.
It is further desirable to provide a magnetostatic wave device comprising first and second mediums suitable for propagating magnetostatic waves which are spaced apart from one another by a plurality of predetermined distances.